The present invention is concerned with vibratile molding machines of the character used in the cement block industry for molding concrete building blocks of varying configuration, and other concrete products such as paving stones and the like, from cement mixes which are vibrated to densify them. Various mechanical vibrator assembles have been utilized to eccentrically provide the vibration for such machines and one such vibrating assembly is disclosed, instance, in the present assignee's U.S. Pat. No. 4,312,242 issued Jan. 26, 1980. In conventional concrete block manufacturing machines, the cycle of operation involves the first step of moving the feed box over the empty mold in the machine and starting the vibrating motor. The motor drives a shaft which eccentrically causes the vibration and the motor continues to be driven during a compacting operation, after which a switch is actuated to stop the electric motor which is used as the drive for the system. At this point a stripper is operated to strip the green blocks from the mold and the pallet which has been clamped to the bottom of the mold is released preparatory to transferring it, and the blocks, to a block curing location.
In prior art machines in which the eccentric shafts producing the vibration have been stopped to halt the vibration at the end of the densifying step, large brakes have been required to stop the shafts. Moreover, because of the rapid acceleration and deceleration required in contemporary high production machines, as much as four times the horsepower required to produce the vibration had to be utilized, with the result that much larger motors and shafts were required for reasons other than producing the vibration. In machinery of the type disclosed in the patent mentioned, the vibrating shaft in effect coasts between intervals of operation of the drive motor and so need not be braked and brought up to full speed from a static position. However, the machine still operates by starting and stopping the drive motor and a substantial acceleration of the coasting shaft is required at the time it is desired to produce vibration. Moreover, such prior art machinery is not versatile in the sense that the amplitude of vibration and the forces exerted can be varied during the vibration portion of the cycle.